1. Field of the Invention
The present invention relates to a portable apparatus with an accelerometer device for free-fall detection. In particular, the following description will make explicit reference to a portable apparatus provided with a mass storage device (hard disk), without this implying any loss of generality.
2. Description of the Related Art
As is known, portable electronic devices, such as for example laptops, PDAs (Personal Data Assistants), digital audio players, cell-phones, digital cameras and the like, can readily be subject to violent impact, in particular in the case where they are dropped on the ground during their normal use. In the event of fall, the impact of the portable apparatus on the ground has a particularly detrimental effect on a hard disk within the portable apparatus, in the worst case producing permanent damage and the consequent loss of the stored data.
Hard disks are very sensitive to impact in so far as the read/write head is normally kept at a very small distance from the data-storage medium. Consequently, in the event of impact, the read/write head strikes the data-storage medium and can be damaged together with it.
In order to prevent, or at least limit, the occurrence of said destructive events, it has been proposed to use linear accelerometers, fixed to the portable apparatus, to detect a free-fall condition of the portable apparatus. Following the free-fall detection, a command is issued for forced parking of the read/write head of the hard disk, which is brought into a safe area of the disk, for example to the position assumed by the head when the apparatus is turned off.
The free-fall condition is detected by appropriate processing of the acceleration signals generated by the accelerometer, and in particular by verifying that the acceleration detected along all the measurement axes is zero.
Linear accelerometer devices are known, built using semiconductor technology, namely the so-called MEMS (Micro-Electro-Mechanical-Systems). As is known, and illustrated in FIG. 1, a linear accelerometer device 1 of a MEMS type includes a sensitive element 2, which detects the acceleration and generates an electrical signal correlated to the detected acceleration, and a conditioning electronics 3 for the conditioning of the electrical signal, which includes a charge integrator 4 and a gain and noise-cancellation stage 5, in particular using the CDS (Correlated Double Sampling) technique.
It is also known that hard-disk manufacturers are reducing the dimensions of the hard disks, in particular in portable devices, wherein the miniaturization of dimensions is of fundamental importance. However, with current technologies, accelerometer devices have large physical dimensions (in particular as regards thickness), which make their integration within the hard disk an issue.
The sensitive element 2 is formed by two distinct portions of semiconductor material (generally silicon): a first portion, in which the microelectromechanical detection structure is formed, and a second portion, which has the function of a protective cap, and is applied to the first portion to seal it hermetically. The microelectromechanical structure must in fact be protected from dust and micrometric corpuscles which could alter its performance and jeopardize its correct operation. The conditioning electronics 3 is bonded on the-surface of the sensitive element 2 whereon contact metallizations are also formed, and electrical connection is obtained using the wire-bonding technique. The conditioning electronics 3 and the sensitive element 2 thus coupled together are coated with a molding resin and enclosed within a package. A structure of the type described cannot have a thickness of less than 1.5 to 2 mm, which prove excessive if compared with the currently required dimensions (a thickness of less than 1.5 mm is required).
The accelerometer devices are currently arranged within the portable apparatus in a position outside the hard disk and are generally coupled to the electronic circuit controlling the general operation of the portable apparatus. Such a solution, however, has problems due to the delays in communication of the free-fall detection signals from the accelerometer device to the hard disk. Consequently, the free-fall condition cannot be detected promptly enough to activate the appropriate actions of protection (for example, the parking of the read/write head) and hence prevent damage to the portable apparatus.